ASGSB 1999 Annual Meeting Abstracts

EXPRESSION OF THROMBIN RECEPTOR IN VASCULAR SMOOTH MUSCLE CELLS IN RESPONSE TO MECHANICAL STIMULATION. K.T. Nguyen, C. Patterson*, M.S. Runge*, S.G. Eskin**, L.V. McIntire. Dept. of Bioeng., Rice Univ.; *Cardiology Division, Univ. of Texas Medical Branch, Galveston;**Dept. of Cell Biology, Texas Biotech Corp.

Space flight can induce changes in forces acting on blood vessels, including cyclic strain due to altered transmural pressure. These forces are important mediators of cellular function in the cardiovascular system. In vivo, thrombin and its receptor (protease activated receptor-1, PAR-1) play important roles in thrombotic and proliferative processes, and are generated and expressed at very high levels in injured arteries. Increased PAR-1 expression associated with local hemodynamic forces might contribute to the cardiovascular risk profile of an individual and to vessel remodeling. Therefore, the objective of this study was to investigate effect of cyclic strain on PAR-1 expression in human aortic smooth muscle cells (HASMCs).

HASMCs were seeded on silicone membranes and subjected to different levels of cyclic strain in a physiological range using our uni-axial strain device. Northern blot analysis showed that high levels of cyclic strain (20% strain at 1 Hertz) increased PAR-1 mRNA levels 2 fold after 6 h of exposure whereas moderate and low strain (10 and 5% strain, respectively) did not affect PAR-1 mRNA in HASMCs. In addition, flow cytometry analysis indicated that high cyclic strain increased surface PAR-1 expression to approximately 250% of static controls. There is increasing evidence that reactive oxygen species (ROS) can act as intracellular second messengers in signal transduction. Treatment of HASMCs with ROS inhibitors, such as N-acetyl-cysteine (NAC) and Pyrrolidinedithiocarbamate (PDTC), decreased cyclic strain-induced PAR-1 expression to 1.1 and 1.4 of static controls, respectively.

These results indicate that cyclic strain up-regulated PAR-1 expression at both mRNA and protein levels, mediated at least in part by ROS. Further studies are underway to investigate specific strain induced enzymatic pathways for ROS generation. In addition, role of protein kinases in cyclic strain-increased PAR-1 expression and functional consequences of changes in PAR-1 expression by cyclic strain on smooth muscle cell function after thrombin exposure, including proliferation, are being examined. (Supported by NASA-NSCORT: NAG5-4072)

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